Explain information for data objects

A single access plan might use one or more data objects to satisfy an SQL or XQuery statement.

Object statistics

The explain facility records information about each object, such as the following:
  • The creation time
  • The last time that statistics were collected for the object
  • Whether or not the data in the object is sorted (only table or index objects)
  • The number of columns in the object (only table or index objects)
  • The estimated number of rows in the object (only table or index objects)
  • The number of pages that the object occupies in the buffer pool
  • The total estimated overhead, in milliseconds, for a single random I/O to the specified table space where the object is stored
  • The estimated transfer rate, in milliseconds, to read a 4-KB page from the specified table space
  • Prefetch and extent sizes, in 4-KB pages
  • The degree of data clustering within the index
  • The number of leaf pages that are used by the index for this object, and the number of levels in the tree
  • The number of distinct full key values in the index for this object
  • The total number of overflow records in the table